Many attempts have been made to provide dentinal sensitivity relief. Stannous ion has been linked to treatment of dentine hypersensitivity. U.S. Pat. No. 5,690,912 teaches that in order for the stannous ion to be efficacious in treating dentine hypersensitivity, it must be stable and freely available and not in chemical combination with other ingredients. The patent discloses an oral hygiene preparation containing SnF2 in combination with 87-97 percent by weight anhydrous glycerin and 2-10 percent by weight polyethylene glycol having an average molecular weight of 1000.
Besides SnF2, other materials generally referred to as “nerve agents” or “nerve desensitizing agents” have been used in the treatment of hypersensitive teeth. Such agents reportedly reduce the excitability of the nerve in a sensitive tooth, and one of the most well-known agents used in commercial dentifrices for sensitive teeth for this purpose is potassium nitrate, and discussed in U.S. Pat. No. 3,863,006. Examples of other agents in this category include other potassium salts such as potassium bicarbonate, potassium chloride and the like, as well as sodium and lithium nitrates.
Another approach to controlling dentinal hypersensitivity is the use of agents to fully or partially occlude tubules. Examples of such “tubule blocking agents” include the following: charged polystyrene beads (U.S. Pat. No. 5,211,939); apatite (U.S. Pat. No. 4,634,589); a polyacrylic acid polymer having a typical molecular weight from about 450,000 to about 4,000,000 (U.S. Pat. No. 5,270,031); and certain clays (U.S. Pat. No. 5,589,159). Still others have attempted to treat dentin sensitivity by inducing the growth of minerals inside the dentinal tubules. A further approach (described in U.S. Pat. Nos. 5,735,942 and 5,891,233) is the use of bioactive glass to treat tooth sensitivity. In general, most of these inventions apparently suffer from problems of fluoride incompatibility and the abrasive nature of these inorganic solids can also be problematic.
The efficacy of fluoride in caries prophylaxis is well established, and topical application of aqueous solutions of various water-soluble fluorides is a rather routine procedure in dental offices and clinics. Toothpaste compositions having certain fluorides have been recognized as effective against caries by the American Dental Association. It is also known that certain metallic ions, for example, stannous fluoride (SnF2), can have a significant effect on the anticariogenic efficacy of fluorides, and has been used in dentistry since the 1950's to treat various oral conditions. Also, in the 1950's, it was reported in scientific literature that the use of a source of stannous ions in conjunctions with fluoride gives a more effective anticariogenic product than is attained with fluoride alone (J. C. Muhler et al., J.A.D.A. 51, 665 (1955)). Topical application of SnF2 has also consistently shown dramatic reductions in dental caries activity with minimal side effect as well as been indicated clinically to be efficacious in the reduction of dentinal hypersensitivity. This latter therapeutic effect is believed to be due, to a large extent, to the stannous ion (Sn2+) component of the salt. More recently, relatively low concentrations of In(III) have been found to coact with fluorides to provide a high level of anticariogenic activity (U.S. Pat. No. 3,175,951, granted Mar. 30, 1965).
U.S. Pat. No. 5,693,314 teaches that attempts to include mixtures of a desensitizing agent such as SnF2 with another desensitizing source such as potassium nitrate, in a single dentifrice composition are of limited effect. Additionally, prolonged contact between Sn2+ and nitrate ion in a single dentifrice results in a reaction of these ions into potentially toxic materials. Thus, the solution is in keeping the two desensitizing sources separate from each other, and combining them for the first time only on the surface of the teeth to avoid any appreciable formation of insoluble tin or reaction product of tin.
U.S. Pat. No. 5,932,192 again teaches a two-component composition of stannous salt and potassium salt, to prevent the stannous compounds from reacting with water and other common oral care ingredients to form insoluble tin. Specific levels of water content within the potassium salt component (at least 44 percent by weight) and the overall water content (at least 22 percent by weight) are said to reduce the astringency, sourness and bitterness of the stannous salt.
U.S. Pat. No. 6,416,745 teaches dental compositions and methods for treating dentinal hypersensitivity based on anionic liposomes that are capable of inducing mineral formation in the dentinal tubules by partially or fully blocking them. The compositions of the liposomes and a suitable carrier are touted to be capable of delivering additional agents useful in the treatment of dentinal hypersensitivity by combining stannous fluoride directly with another desensitizing agent to further take advantage of the known anticariogenic and anti-microbial action of SnF2.
Thus, it is clear that those skilled in the relevant art recognize that in order to capture the efficacy of stannous fluorides when additional desensitizing agents are added to an over-the-counter composition, either a 2-component system or agents such as liposomes are needed.
Therefore, there remains a need for a one-component composition having fluoride efficacy and sensitivity relief that a dental professional can easily administer to the teeth of patients during office visits.